Analysis of Climate Change Impact on Water Supply in Northern Istria (Croatia)
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ISSN 1330-3651 (Print), ISSN 1848-6339 (Online) https://doi.org/10.17559/TV-20170809140304 Original scientific paper Analysis of Climate Change Impact on Water Supply in Northern Istria (Croatia) Barbara KARLEUŠA, Josip RUBINIĆ, Maja RADIŠIĆ, Nino KRVAVICA Abstract: This paper analyses impacts of climate change and anthropogenic pressure on groundwater resources in the Mirna river catchment used for water supply in Northern Istria (Croatia) up to 2050. Using Regional Climate Models simulations and hydrologic model, the future average annual and the characteristic (in critical period) water resource availabilities were calculated. Current and five future water demand scenarios were analysed. Water Exploitation Index (WEI) and modified Characteristic Water Exploitation Index (CWEI) were calculated. In 2050, the analysed springs will be subject to climate change consequences, with more extreme changes and intense variations. The WEI for average conditions indicates little risk of unmet future water demand. Considering seasonal variability, the future CWEIs indicates strong risk for most future water demand scenarios and overexploitation for water demand increases over 20%. The 2012 drought, more extreme than any considered future scenario, was also examined. Keywords: climate change; drinking water supply; water resources availability 1 INTRODUCTION Regardless of the methodology used to simulate climate change, the impact of climate change on the water The Mediterranean basin, including the Adriatic Sea resources in the Mediterranean has been confirmed in region, is a region that is very sensitive to climate change different studies [13-15]. Based on scenarios of varying and anthropogenic impacts [1]. According to Xoplaki et al. future temperature and precipitation to analyse the changes [2], since the 1970s, the mean annual temperatures in the in groundwater recharge and in agricultural water demand Mediterranean region have increased by 0.1 °C per decade, for the West Bank of the Mediterranean basin, Mizyed 15] and precipitation has decreased by 25 mm per decade. concluded that the groundwater recharge could decrease by Temperatures are expected to increase by 1.5-2.5°C, and up to 50%. precipitation is expected to decrease by 5% to 20% up to Water supply system and sources vulnerability due to 2050 [3], which could significantly decrease (30-50%) climate change are analysed by researchers in the freshwater resources throughout the Mediterranean basin. Monterrey Metropolitan Area of northern Mexico [7] and In the Adriatic region, the decrease of 15% of freshwater is on Mexico City [16]. However, only a small number of expected in northern Italy and the Balkans [3]. Climate papers have investigated mitigation measures and adaptive changes cause more frequent drought and flood strategies for drinking water supply [4, 17]. occurrence. On the other hand, an increase in water Impact of climate change on water resources used for demand is expected due to increasing urbanisation, drinking water supply in the Adriatic region has been agricultural production and tourism activities, increasing investigated within the DRINKADRIA project [18, 19]. the withdrawal of and pressures on regional water This paper presents the investigation of the climate resources [4]. Changes in land use potentially affect the change impacts and the anthropogenic pressure on available water resources too (e.g. increased intercepted groundwater resources in the river Mirna catchment that precipitation in case of enlarging the forest area [5]). are used for drinking water supply in Northern Istria Water resource and supply vulnerability and risk (Croatia, Northern part of the Adriatic sea region) to give assessments, water scarcity estimates and drought analyses the basis for preparation of adaptation and mitigation due to climate change impacts are necessary for avoiding strategies up to year 2050. Analysing the impacts of future water crises and preparing adaptation measures to climate change on water resource availability consists of mitigate the consequences of such crises [6,7]. using RCMs to simulate the change in temperature and Numerous studies have investigated the impact of precipitation up to 2050. Then, based on the results from climate change on water resources worldwide (e.g. [8]); climate modelling, a hydrological model is applied to many have also analysed the impacts of human activities calculate the future average annual water resource on water resources (e.g. [9]). Recently, more research has availability and characteristic renewable water resources been conducted to simulate the impacts of climate change availability (critical period), which are compared to past on water resources in future. This can be done by using availability to estimate the changes. various methodologies [10]: coupling Global Circulation Water demand analysis was conducted for the present Models (GCMs) with hydrologic models through demand and for five future water demand scenarios. To downscaling techniques, coupling high-resolution estimate the water resource vulnerability in Northern Istria, Regional Climate Models (RCMs) with hydrologic models the Water Exploitation Index (WEI) was calculated [20]. and using hypothetical scenarios as inputs to hydrologic However, to encompass the strong seasonal variability of models. Coupling high-resolution RCMs with hydrologic the water demand and water resource availability, a models has frequently been used to model the climate modified Characteristic Water Exploitation Index (CWEI) change impacts on hydrological regimes and water was also used. resources in the mid- to long-term future in Europe [11, The 2012 drought, which was more extreme than any 12]. considered future scenario, was also examined. 366 Technical Gazette 25, Suppl. 2(2018), 366-374 Barbara KARLEUŠA et al.: Analysis of Climate Change Impact on Water Supply in Northern Istria (Croatia) 2 STUDY AREA The area of the Mirna catchment is most significant in terms of the available groundwater and surface water The river Mirna catchment is the largest drainage basin resources included in the water supply system of Istarski and watercourse in the Istria peninsula and covers vodovod (Water Utility of Istria), the largest of the three approximately 700 km2 (Fig. 1). water supply companies in Istria County. Using spring water for water supply adds pressure to the water resources and the ecosystem of the Mirna River, particularly during the extremely dry years that are becoming increasingly more frequent. The coastal area that is supplied by these springs mostly host tourist activity, leading to increased water demand in the summer months, when the spring yield is the lowest. Severe dry events during the last several decades (e.g., 1986-89, 2002-03, and 2011-12) have shown that the exploitable water resources available in Istria within the constructed water supply systems are at the limit of meeting the current needs. A potential solution is to better optimise the provision of seasonal water reserves from the Butoniga reservoir (45°19'57.8" N 13°55'25.3" E), which also lies in the Mirna catchment (Fig. 1). This reservoir has a volume of approximately 20 million m3, 8 million m3 of Figure 1 Mirna River catchment and location of springs Sv. Ivan, Bulaž and water is used for water supply annually. Gradole and Butoniga reservoir Due to the proximity of the individual spring catchments and the close occurrences of both wet and dry The area of Istrian Peninsula is spreading over 3476 2 2 periods, the water balance characteristics of these three km , of which 2820 km administratively belongs to Istria most significant spring water intakes in this area (i.e., Sv. County. The Mirna catchment area belongs to the Ivan, Gradole and Bulaž) are presented and analysed in the periphery of the Adriatic Carbonate platform. This aggregate in this paper (Fig. 2). geological structure includes carbonate and clastic deposits with stratigraphic ranges from the Upper Jurassic to the Eocene. The parts of the Istrian Peninsula where the surface watercourses are developed are mostly composed of flysch. The northern and northeastern parts of Istria are characterized by significant structural disturbances of the high carbonate massif of Mt Učka and Mt Ćićarija. The central and southeastern parts of Istria belong to the Pazin flysch basin, while the northwestern edge of this area belongs to the Trieste flysch basin. The Buje carbonate anticline rises between these basins, while the western and southwestern parts belong to the western Istrian carbonate anticline. The Mirna River formed its course between the abovementioned structures and partly through a valley area composed of an alluvial deposit reaching deep below sea level, thus retarding groundwater flow. Groundwater emerges from the aquifer, in the form of several significant karst springs in the Mirna catchment at a contact point between the karst hinterland and the alluvial deposits. These springs are Sv. Ivan in the upper Mirna course (45°24'03.2" N 13°58'39.5" E), Bulaž in its middle course (45°22'46.5" N 13°53'17.4" E), and Gradole in its lower course (45°20'37.9" N 13°42'10.9" E) (Fig. 1). The already observed manifestations of climate change are predicted to intensify in this area, where the majority of Figure 2 Distribution of: a) the average monthly discharge and abstracted flow run-off goes underground, and karst springs are the main of Sv. Ivan, Gradole and Bulaž springs and Butoniga reservoir (2003-2014); b) water supply resource